Long built on tradition and bipartisanship, the presidential transition exploded into a point of political contention four years ago, after then-President Donald Trump made baseless claims to dispute his loss and his administration delayed kicking off the transition process for weeks.

This year, a new law is meant to start the transition sooner, no matter who wins. But, if neither major party candidate concedes after Election Day, the updated rules allow both sides to get additional government funding and logistical support to begin working toward transitioning to power. That could lead to both Vice President Kamala Harris and Trump potentially assembling dueling, governments-in-waiting for weeks.

"Rules can only take you so far, and ultimately you need to have the players in the system working to shared objective," said Max Stier, president and CEO of the nonprofit Partnership for Public Service, which has worked with candidates and incumbents on transitions. "Everyone should have the shared objective of making sure that the handoff of power is smooth and effective. And that requires a cooperation that law can't alone enforce."

Here's a look at how changes meant to fix the problems of four years ago may not solve coming issues this time, and where the coming transition stands in the meantime:

What happened in 2020?

Trump lied about widespread voter fraud that didn't occur, delaying the start of the 2020 transition from one administration to the next from Election Day on Nov. 3 to Nov. 23.

The Trump-appointed head of the General Services Administration, Emily Murphy, consulted the transition law dating to 1963 and determined that she had no legal standing to determine a winner -- and start funding and cooperating with a transition to a Biden administration -- because Trump was still challenging the results in court.

GSA essentially acts as the federal government's landlord, and it wasn't until Trump's efforts to subvert free and fair election results had collapsed across key states that Murphy agreed to formally " ascertain a president-elect " and begin the transition process. Trump also eventually posted on social media that his administration would cooperate.

What's different this time?

Enacted in December 2022, the Presidential Transition Improvement Act now mandates that the transition process begin five days after the election, even if more than one candidate hasn't conceded.

That avoids long delays and means "an 'affirmative ascertainment' by the GSA is no longer a prerequisite for gaining transition support services," according to agency guidelines on the new rules.

But the new law also effectively mandates federal support and cooperation for both candidates to begin a transition. It states that such support should continue until "significant legal challenges" that could alter electoral outcomes have been "substantially resolved," or when electors from each state meet in December to formally choose an Electoral College winner.

That means the government potentially bestowing enough backing that both sides can prepare an administration until mid-December -- only about a month before Inauguration Day on Jan. 20.

Derek Muller, a University of Notre Dame law professor and presidential transition expert who testified in favor of the legislation, said it ensures that potentially two candidates get backing for transitions, with one eventually falling away. He said that's preferable to having a situation where no transition support is released to either side -- which can spark delays leading to national security lapses.

"In the past, it was neither candidate gets the funding. Now it's both," Muller said.

He pointed to the contested 2000 election, when GSA didn't determine the winner until the Florida recount fight was settled on Dec. 13 -- raising questions about national security gaps that may have contributed to the U.S. being underprepared for the Sept. 11 attacks the following year.

"It can last into mid-December. There's no question that's a risk," Muller said of potential dueling transition efforts after this year's election. "But I think it's a risk that they want to take. And even mid-December is still a month away from inauguration, so at least you have some certainty."

Even today, though, Trump continues to falsely claim he won in 2020 and only says he'll accept this November's results if they are fair, making it easy to imagine him doing so only if he wins -- and potentially putting the new law to the test.

How are both sides preparing?

The sprawling transition process starts around 4,000 government positions being filled with political appointees -- people who are specifically tapped for their jobs by the president-elect's team. That often begins with key Cabinet departments.

Harris' team already has reached an agreement with the Biden administration to use government office space in Washington and other resources, and to begin vetting potential key national security hires.

Trump's team has signed no transition agreements, missing deadlines to agree with GSA on logistical matters like office space and tech support and with the White House on access to agencies, including documents, employees and facilities.

Stier, of the Partnership for Public Service, said the Trump administration's disregard for the transition process dates to 2016, when the then-president-elect fired his transition coordinator, former New Jersey Gov. Chris Christie, and then spent months of his early administration trying to catch up on basic staffing issues.

Stier said the agreements to prepare transition are merely "the starter's pistol -- it isn't actually the race." The full process, he said, "requires a deep understanding of our government and a willingness to appreciate the importance of process."

What will transition look like?

Neither side will be starting totally from scratch. While Harris will build her own government, she might tap some holdovers from the Biden administration, where she was vice president. Trump will bring in a new team, but he built an entirely new administration in 2017 and can do it again.

Harris could also opt to keep Senate-confirmed Biden appointees as acting Cabinet secretaries, just in case it is hard to get her nominations through a post-election, GOP-controlled Congress. She's promised to appoint a Republican to her Cabinet, with an early favorite being former Wyoming Rep. Liz Cheney -- once the third-ranking member of the House GOP and the daughter of a Republican vice president -- who has campaigned with Harris.

Trump said he may tap former independent presidential hopeful and anti-vaccination activist Robert Kennedy Jr. on health issues and make South African-born Elon Musk a secretary of federal "cost-cutting."

Either way, John Kirby, Biden's national security spokesman, said the current administration is set for a proper transition, ?no matter how things play out in the election."